Detection and evaluation of immunofunction of patients with severe fever with thrombocytopenia syndrome

Current insights into human pathogenic phenuiviruses and the host immune system

Phenuiviruses are a class of segmented negative-sense single-stranded RNA viruses, typically consisting of three RNA segments that encode four distinct proteins. The emergence of pathogenic phenuivirus strains, such as Rift Valley fever phlebovirus (RVFV) in sub-Saharan Africa, Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV) in East and Southeast Asia, and Heartland Virus (HRTV) in the United States has presented considerable challenges to global public health in recent years. The innate immune system plays a crucial role as the initial defense mechanism of the host against invading pathogens. In addition to continued research aimed at elucidating the epidemiological characteristics of phenuivirus, significant advancements have been made in investigating its viral virulence factors (glycoprotein, non-structural protein, and nucleoprotein) and potential host-pathogen interactions. Specifically, efforts have focused on understanding mechanisms of viral immune evasion, viral assembly and egress, and host immune networks involving immune cells, programmed cell death, inflammation, nucleic acid receptors, etc. Furthermore, a plethora of technological advancements, including metagenomics, metabolomics, single-cell transcriptomics, proteomics, gene editing, monoclonal antibodies, and vaccines, have been utilized to further our understanding of phenuivirus pathogenesis and host immune responses. Hence, this review aims to provide a comprehensive overview of the current understanding of the mechanisms of host recognition, viral immune evasion, and potential therapeutic approaches during human pathogenic phenuivirus infections focusing particularly on RVFV and SFTSV.

Recent research advances in the development of Dabie Banda virus vaccines

Severe fever with thrombocytopenia syndrome (SFTS) is a newly identified tick-borne viral hemorrhagic fever caused by Dabie Banda virus (DBV). The virus was first discovered in eastern China in 2009 and is now considered an infectious disease with a mortality rate ranging from 6.3% to 30%. The best strategy for controlling SFTS is to develop effective vaccines. However, no approved vaccines are currently available to prevent this disease, despite the number of extensive and in-depth studies conducted on DBV in the past few years. This review focuses on the structure of DBV and the induced host immune responses which are the fundamental factors in vaccine development, and thoroughly summarizes the current research progress on DBV vaccines. The developing DBV vaccines include protein subunit vaccines, live attenuated vaccines, recombinant virus vector vaccines, and DNA vaccines. At present, almost all candidate vaccines for DBV are in the laboratory development or preclinical stages. There remain challenges in successfully developing clinically approved DBV vaccines.

Cytokines and lymphocyte subsets are associated with disease severity of severe fever with thrombocytopenia syndrome

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by severe fever with thrombocytopenia syndrome virus (SFTSV). Previous studies have indicated that SFTS patients have a high mortality rate, which may be related to cytokine storm and immune dysfunction. In our study, we analyzed differences in cytokines and lymphocyte subsets between severe and non-severe SFTS patients, with the aim of identifying predictors of severity.

METHODS

We retrospectively analyzed demographic characteristics, clinical data, cytokine profiles, and lymphocyte subsets from 96 laboratory confirmed SFTS patients between April 2021 and August 2023.

RESULTS

A total of 96 SFTS patients were enrolled, with a mean age of 65.05 (± 7.92) years old. According to our grouping criteria, 35 (36.5%) of these patients were classified as severe group, while 61 (63.5%) were classified as non-severe group. Univariate analysis revealed that age, interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-10 (IL-10), interferon-α (IFN-α), CD4 + T cell, and CD8 + T cell counts were risk predictors for the severity of SFTS. Further multivariable logistic regression analysis confirmed age, IL-6 levels, and CD4 + T cell counts as independent predictors of SFTS severity.

CONCLUSIONS

Severe SFTS patients may experience cytokine storms and immune dysfunction. Aging, elevated levels of IL-6, and decreased CD4 + T cell count may serve as independent predictors for the severity of SFTS.

Antiviral immunity of severe fever with thrombocytopenia syndrome: current understanding and implications for clinical treatment

Dabie Banda virus (DBV), a tick-borne pathogen, was first identified in China in 2009 and causes profound symptoms including fever, leukopenia, thrombocytopenia and multi-organ dysfunction, which is known as severe fever with thrombocytopenia syndrome (SFTS). In the last decade, global incidence and mortality of SFTS increased significantly, especially in East Asia. Though previous studies provide understandings of clinical and immunological characteristics of SFTS development, comprehensive insight of antiviral immunity response is still lacking. Here, we intensively discuss the antiviral immune response after DBV infection by integrating previous ex- and in-vivo studies, including innate and adaptive immune responses, anti-viral immune responses and long-term immune characters. A comprehensive overview of potential immune targets for clinical trials is provided as well. However, development of novel strategies for improving the prognosis of the disease remains on challenge. The current review may shed light on the establishment of immunological interventions for the critical disease SFTS.

The Adaptive Immune Response against Bunyavirales

The Bunyavirales order includes at least fourteen families with diverse but related viruses, which are transmitted to vertebrate hosts by arthropod or rodent vectors. These viruses are responsible for an increasing number of outbreaks worldwide and represent a threat to public health. Infection in humans can be asymptomatic, or it may present with a range of conditions from a mild, febrile illness to severe hemorrhagic syndromes and/or neurological complications. There is a need to develop safe and effective vaccines, a process requiring better understanding of the adaptive immune responses involved during infection. This review highlights the most recent findings regarding T cell and antibody responses to the five Bunyavirales families with known human pathogens (Peribunyaviridae, Phenuiviridae, Hantaviridae, Nairoviridae, and Arenaviridae). Future studies that define and characterize mechanistic correlates of protection against Bunyavirales infections or disease will help inform the development of effective vaccines.

Inhibition of SFTSV replication in humanized mice by a subcutaneously administered anti-PD1 nanobody

Severe fever with thrombocytopenia syndrome (SFTS) is a life-threatening disease caused by a novel bunyavirus (SFTSV), mainly transmitted by ticks. With no effective therapies or vaccines available, understanding the disease's mechanisms is crucial. Recent studies found increased expression of programmed cell death-1 (PD-1) on dysfunctional T cells in SFTS patients. However, the role of the PD-1/programmed cell death-ligand 1 (PD-L1) pathway in SFTS progression remains unclear. We investigated PD-1 blockade as a potential therapeutic strategy against SFTSV replication. Our study analyzed clinical samples and performed in vitro experiments, revealing elevated PD-1/PD-L1 expression in various immune cells following SFTSV infection. An anti-PD-1 nanobody, NbP45, effectively inhibited SFTSV infection in peripheral blood mononuclear cells (PBMCs), potentially achieved through the mitigation of apoptosis and the augmentation of T lymphocyte proliferation. Intriguingly, subcutaneous administration of NbP45 showed superior efficacy compared to a licensed anti-PD-1 antibody in an SFTSV-infected humanized mouse model. These findings highlight the involvement of the PD-1/PD-L1 pathway during acute SFTSV infection and suggest its potential as a host target for immunotherapy interventions against SFTSV infection.

Lethal severe fever with thrombocytopenia syndrome virus infection causes systemic germinal centre failure and massive T cell apoptosis in cats

Introduction

Severe fever with thrombocytopenia syndrome (SFTS) is a fatal viral disease characterized by high fever, thrombocytopenia, leukopenia, and multi-organ haemorrhage. Disruption of the humoral immune response and decreased lymphocyte numbers are thought to contribute to the disease severity. These findings have been obtained through the analysis of peripheral blood leukocytes in human patients, whereas analysis of lymph nodes has been limited. Thus, in this study, we characterized the germinal centre response and apoptosis in the lymph nodes of cats with fatal SFTS, because SFTS in cats well mimics the pathology of human SFTS.

Methods

Lymph node tissue sections collected during necropsy from seven fatal SFTS patients and five non-SFTS cases were used for histopathological analysis. Additionally, lymph node tissue sections collected from cats with experimental infection of SFTS virus (SFTSV) were also analysed.

Results

In the lymphoid follicles of cats with SFTS, a drastic decrease in Bcl6- and Ki67-positive germinal centre B cells was observed. Together, the number of T cells in the follicles was also decreased in SFTS cases. In the paracortex, a marked increase in cleaved-caspase3 positivity was observed in T cells. These changes were independent of the number of local SFTS virus-positive cell. Furthermore, the analysis of cats with experimental SFTSV infection revealed that the intrafollicular Bcl6- and CD3-positive cell numbers in cats with low anti-SFTSV antibody production were significantly lower than those in cats with high anti-SFTSV antibody production.

Discussion

These results suggest that dysfunction of the humoral response in severe SFTS was caused by the loss of germinal centre formation and massive apoptosis of T cells in the lymph nodes due to systemically circulating viruses.

Clinical characteristics of severe fever with thrombocytopenia syndrome (SFTS) sepsis and non-SFTS sepsis

Severe fever with thrombocytopenia syndrome (SFTS) is a new infectious disease caused by bunyavirus, and the critically cases conform to the definition of sepsis. In order to compare the differences between SFTS sepsis and non-SFTS sepsis, a retrospective analysis was performed. Thirty-seven SFTS sepsis and 96 non-SFTS sepsis patients were enrolled. The clinical characteristics, laboratory results were compared between the two groups and independent prognostic risk of mortality were investigated respectively. Compared with non-SFTS sepsis, SFTS cases had lower white blood cell, neutrophil and platelet counts, prolonged activated partial thromboplastin time and decreased fibrinogen, slightly elevated inflammatory indicators. Interleukin-6 (IL-6), and acute physiology and chronic health evaluation Ⅱ (APACHE II) score were independent prognostic risk factors in non-SFTS sepsis. The mortality risk of STFS sepsis was related to the viral clearance. There was no difference in viral load between SFTS survivors and non-survivors on admission. However, the differences were significant on 5th, 7th, 10th, and 14th day, and all SFTS non-survivors died within 14 days. Viral clearance rate on 7th day was an independent risk factor for mortality in SFTS sepsis. The mortality risk of STFS sepsis was related to the viral clearance rate.

Evaluation of reverse transcription loop-mediated isothermal amplification assay for the detection of severe fever with thrombocytopenia syndrome in clinical laboratories: A single-center study

Severe fever with thrombocytopenia syndrome (SFTS) is an acute infectious disease prevalent in East Asia with a high mortality rate (5%-30%). Reverse transcription loop-mediated isothermal amplification (RT-LAMP), a rapid nucleic acid-based diagnostic technique, is a useful alternative for the clinical diagnosis of SFTS, particularly in resource-limited hospitals or rural clinics in SFTS virus-endemic regions. However, the actual clinical sensitivity and specificity of RT-LAMP remain unclear. This study evaluated the field application of RT-LAMP. This prospective field study included 130 patients with laboratory-confirmed SFTS from Yantai, Shandong Province, China. Two sets of RT-LAMP primers were validated, and one set of RT-LAMP assays was optimized for field detection. Nucleic acids of serially collected serum/plasma samples were identified using quantitative reverse transcription polymerase chain reaction (RT-qPCR) and RT-LAMP. In laboratory tests, we optimized the detection time of primer set 2 for the RT-LAMP to 60 min. Notably, the onsite testing of 279 plasma samples from patients with SFTS revealed that the sensitivity and specificity of the test were 81.9% and 96.3%, respectively. We also analyzed samples with different durations of the disease, and our study showed that the sensitivity of RT-LAMP detection at the beginning of admission was 89.92%. Univariate analysis showed that the detection rate of RT-LAMP was similar to that of RT-qPCR in the first 5 days of the disease course and was lower than that of RT-qPCR on Days 6 and 14-15 of the disease course. The positive detection rate in patients aged ≥ 65 years was significantly higher than that in younger age groups. RT-LAMP is a simple, suitable, and rapid clinical detection method of SFTS onsite screening. It is more suitable for screening patients in the early stages of the disease and analyzing samples obtained from patients aged ≥ 65 years before the 6th day of the disease course.

Effect of intravenous immunoglobulin therapy on the prognosis of patients with severe fever with thrombocytopenia syndrome and neurological complications

Background

Intravenous immunoglobulin (IVIG) has been reported to exert a beneficial effect on severe fever with thrombocytopenia syndrome (SFTS) patients with neurological complications. However, in clinical practice, the standard regime is unclear and there is a lack of evidence from large-scale studies.

Methods

A single-center retrospective study was conducted to determine the influence of IVIG dosage and duration on SFTS patients with neurological complications. The primary outcome was 28-day mortality, and laboratory parameters before and after IVIG treatment were measured. Survival curves were generated using the Kaplan-Meier method and analyzed with the log-rank test according to the median IVIG dosage and IVIG duration. Besides, multivariate Cox regression analysis was performed to examine the association between the independent factors and 28-day mortality in SFTS patients.

Results

Overall, 36 patients (58.06%) survived, while 26 (41.9%) patients died. The median age of the included patients was 70 (55-75) years, and 46.8% (29/62) were male. A significantly higher clinical presentation of dizziness and headache was observed in the survival group. The IVIG duration in the survival group was longer than in the death group (P <0.05). Additionally, the IVIG dosage was higher in the survival group than in the death group, but there was not a statistically significant difference between the two groups (P = 0.066). The mediating effect of IVIG duration was verified through the relationship between IVIG dosage and prognosis using the Sobel test. Univariate analysis revealed that IVIG dosage (HR: 0.98; 95% CI: 0.97-1.00; P = 0.007) and IVIG duration (HR: 0.54; 95% CI: 0.41-0.72; P <0.001) were significantly associated with risk of death. The multivariate analysis generated an adjusted HR value of 0.98 (95% CI: 0.96-1.00; P = 0.012) for IVIG dosage and 0.26 (95% CI: 0.09-0.78; P = 0.016) for dizziness and headache.

Conclusion

Prolonged high-dose IVIG is beneficial to the 28-day prognosis in SFTS patients with neurological complications.

The clinical and immunological characteristics in fatal severe fever with thrombocytopenia syndrome virus (SFTSV) infection

OBJECTIVE

This study aimed to make a comprehensive evaluation of peripheral immune profiles for further understanding the immunopathogenesis of severe fever with thrombocytopenia syndrome (SFTS).

METHODS

Forty-seven patients with SFTS virus infection were included, of which 24 were deceased. The percentages, absolute numbers, phenotype of lymphocyte subsets were detected by flow cytometry.

RESULTS

In patients with SFTS, the numbers of CD3+T, CD4+T, CD8+T and NKT cells were decreased compared with healthy controls (HCs), accompanied with highly active and exhausted phenotypes for T cells, and overproliferating plasmablasts. High inflammatory status, dysregulation of coagulation and host immune response were more obvious in deceased patients than that of survivors. Higher levels of PCT, IL-6, IL-10, TNF-α, APTT, TT and the occurrence of hemophagocytic lymphohistiocytosis were poor prognostic indicators of SFTS.

CONCLUSIONS

The evaluation of immunological markers in combination with laboratory tests has critical value for selecting prognostic markers and potential treatment target.

Severe fever with thrombocytopenia syndrome virus trends and hotspots in clinical research: A bibliometric analysis of global research

Background

Since severe fever with thrombocytopenia syndrome virus (SFTSV) was first reported in 2009, a large number of relevant studies have been published. However, no bibliometrics analysis has been conducted on the literature focusing on SFTSV. This study aims to evaluate the research hotspots and future development trends of SFTSV research through bibliometric analysis, and to provide a new perspective and reference for future SFTSV research and the prevention of SFTSV.

Methods

We retrieved global publications on SFTSV from the Web of Science Core Collection (WoSCC) and Scopus databases from inception of the database until 2022 using VOSviewer software and CiteSpace was used for bibliometric analysis.

Results

The number of SFTSV-related publications has increased rapidly since 2011, peaking in 2021. A total of 45 countries/regions have published relevant publications, with China topping the list with 359. The Viruses-Basel has published the most papers on SFTSV. In addition, Yu et al. have made the greatest contribution to SFTSV research, with their published paper being the most frequently cited. The most popular SFTSV study topics included: (1) pathogenesis and symptoms, (2) characteristics of the virus and infected patients, and (3) transmission mechanism and risk factors for SFTSV.

Conclusions

In this study, we provide a detailed description of the research developments in SFTSV since its discovery and summarize the SFTSV research trends. SFTSV research is in a phase of explosive development, and a large number of publications have been published in the past decade. There is a lack of collaboration between countries and institutions, and international collaboration and exchanges should be strengthened in the future. The current research hotpots of SFTSV is antiviral therapy, immunotherapy, virus transmission mechanism and immune response.

High C-reactive protein to lymphocyte ratio predicts mortality outcomes of patients with severe fever with thrombocytopenia syndrome: A multicenter study in China

Severe fever with thrombocytopenia syndrome (SFTS) is a life-threatening infectious disease caused by the SFTS virus (SFTSV). This study aimed to evaluate the predictive power of C-reactive protein to lymphocyte ratio (CLR) and establish an early-warning model for SFTS mortality. We retrospectively analyzed hospitalized SFTS patients in six clinical centers from May 2011 to 2022. The efficacy of CLR prediction was evaluated by the receiver operating characteristic (ROC) analysis. A nomogram was established and validated. Eight hundred and eighty-two SFTS patients (median age 64 years, 48.5% male) were enrolled in this study, with a mortality rate of 17.8%. The area under the ROC curve (AUC) of CLR was 0.878 (95% confidence interval [CI]: 0.850-0.903, p < 0.001), which demonstrates high predictive strength. The least absolute shrinkage and selection operator regression selected seven potential predictors. Multivariate logistic regression analysis determined three independent risk factors, including CLR, to construct the nomogram. The performance of the nomogram displayed excellent discrimination and calibration, with significant net benefits in clinical uses. CLR is a brand-new predictor for SFTS mortality. The nomogram based on CLR can serve as a convenient tool for physicians to identify critical SFTS cases in clinical practice.

Investigation of predictors for invasive pulmonary aspergillosis in patients with severe fever with thrombocytopenia syndrome

Patients with severe fever with thrombocytopenia syndrome (SFTS) had been confirmed to have immune dysfunction and were prone to invasive pulmonary aspergillosis (IPA), which was directly related to the increased mortality. The aim of this study was to investigate the predictors for IPA in SFTS patients, and the results were expected to be helpful for early identification of IPA and initiation of anti-fungal therapy. The study was performed to review laboratory confirmed SFTS patients in two tertiary hospitals in Shandong province (Qilu Hospital of Shandong University and Shandong Public Health Clinical Center) from April 2021 to August 2022. The enrolled patients were further divided into IPA group and non-IPA group. Demographic characteristics, clinical manifestations and laboratory parameters between IPA group and non-IPA group patients were analyzed and compared to identify the independent predictors for IPA by univariate analysis and multivariable logistic regression analysis. Sensitivity and specificity of independent predictors were evaluated by receiver operating characteristic (ROC) curve analysis. In total, 67 SFTS patients were enrolled with an average age of 64.7 (± 8.4) years old. The incidence of IPA was 32.8% (22/67). Mortality of patients in IPA group was 27.3% (6/22), which was significantly higher than that in non-IPA group. Results of univariate analysis showed that uncontrolled diabetes, central nervous system symptoms, platelet < 40 × 109/L, CD4+ T cell < 300/μL and CD8+ T cell < 400/μL were risk factors for development of IPA. These factors were further analyzed by multivariable logistic regression analysis and the results indicated that uncontrolled diabetes, platelet < 40 × 109/L, CD4+ T cell < 300/μL and CD8+ T cell < 400/μL could be recognized as independent predictors for IPA in SFTS patients. In conclusion, IPA is a serious complication for SFTS patients and increases mortality. It is necessary to early identify predictors of IPA for improving survival of SFTS patients.

Longitudinal analysis of immunocyte responses and inflammatory cytokine profiles in SFTSV-infected rhesus macaques

Severe fever with thrombocytopenia syndrome virus (SFTSV), an emerging bunyavirus, causes severe fever with thrombocytopenia syndrome (SFTS), with a high fatality rate of 20%-30%. At present, however, the pathogenesis of SFTSV remains largely unclear and no specific therapeutics or vaccines against its infection are currently available. Therefore, animal models that can faithfully recapitulate human disease are important to help understand and treat SFTSV infection. Here, we infected seven Chinese rhesus macaques (Macaca mulatta) with SFTSV. Virological and immunological changes were monitored over 28 days post-infection. Results showed that mild symptoms appeared in the macaques, including slight fever, thrombocytopenia, leukocytopenia, increased aspartate aminotransferase (AST) and creatine kinase (CK) in the blood. Viral replication was persistently detectable in lymphoid tissues and bone marrow even after viremia disappeared. Immunocyte detection showed that the number of T cells (mainly CD8⁺ T cells), B cells, natural killer (NK) cells, and monocytes decreased during infection. In detail, effector memory CD8⁺ T cells declined but showed increased activation, while both the number and activation of effector memory CD4⁺ T cells increased significantly. Furthermore, activated memory B cells decreased, while CD80⁺/CD86⁺ B cells and resting memory B cells (CD27⁺CD21⁺) increased significantly. Intermediate monocytes (CD14⁺CD16⁺) increased, while myeloid dendritic cells (mDCs) rather than plasmacytoid dendritic cells (pDCs) markedly declined during early infection. Cytokines, including interleukin-6 (IL-6), interferon-inducible protein-10 (IP-10), and macrophage inflammatory protein 1 (MCP-1), were substantially elevated in blood and were correlated with activated CD4⁺ T cells, B cells, CD16⁺CD56⁺ NK cells, CD14⁺CD16⁺ monocytes during infection. Thus, this study demonstrates that Chinese rhesus macaques infected with SFTSV resemble mild clinical symptoms of human SFTS and provides detailed virological and immunological parameters in macaques for understanding the pathogenesis of SFTSV infection.

CD8+ T cells mediate antiviral response in severe fever with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS), which is caused by a novel Bunyavirus, has gradually become a threatening infectious disease in rural areas of Asia. Studies have identified a severe cytokine storm and impaired humoral immune response in SFTS. However, the cellular immune response to SFTS virus (SFTSV) infection remains largely unknown. Here we report that SFTS patients had a cytokine storm accompanied by high levels of chemokines. CD8⁺ T cells in peripheral blood mononuclear cells of SFTS patients exhibited a more activated phenotype and enhanced the antiviral responses. They increased the expression of CD69 and CD25, secreted a higher level of IFN-γ and granzyme, and had a stronger proliferative ability than in healthy controls. In convalescent SFTS patients, the expression of CD69 and CD25 on CD8⁺ T cells was reduced. In addition, we found the ratio and cellularity of CD14⁺ CD16⁺ intermediate monocytes were increased in peripheral blood of SFTS patients. Both the expression of C-X-C motif chemokine ligand 10 (CXCL10) on CD14⁺ CD16⁺ intermediate monocytes and the expression of C-X-C motif chemokine receptor 3 (CXCR3) on CD8⁺ T cells increased dramatically in SFTS patients. Our studies reveal a potential pathway that CD8⁺ T cells rapidly activate and are mostly recruited by intermediate monocytes through CXCL10 in SFTSV infection. Our results may be of clinical relevance for further treatment and discharge instructions in SFTSV infections.

Ferritin and procalcitonin serve as discriminative inflammatory biomarkers and can predict the prognosis of severe fever with thrombocytopenia syndrome in its early stages

Introduction

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with high mortality. The pathophysiology of SFTS remains unclear. Hence, the identification of inflammatory biomarkers for SFTS is crucial for the timely management and prevention of disease severity.

Methods

A total of 256 patients with SFTS were divided into a survivor group and a non-survivor group. Classical inflammatory biomarkers such as ferritin, procalcitonin (PCT), C-reactive protein (CRP), and white blood cells were investigated for their association with viral load and the clinical significance for predicting the mortality of patients with SFTS.

Results

Serum ferritin and PCT showed a positive association with viral load. Ferritin and PCT levels in non-survivors were significantly higher than those in survivors at 7-9 days from symptom onset. The area under the receiver operating characteristic curve (AUC) values of ferritin and PCT for predicting the fatal outcome of SFTS were 0.9057 and 0.8058, respectively. However, the CRP levels and WBC counts exhibited a weak association with viral load. The AUC value of CRP for predicting mortality was more than 0.7 at 13-15 days from symptom onset.

Discussion

Ferritin and PCT levels, especially ferritin, could be potential inflammatory biomarkers for predicting the prognosis of patients with SFTS in its early stages.

Clinical features and epidemiology of severe fever with thrombocytopenia syndrome in dogs in the Republic of Korea: an observational study (2019-2020)

Severe fever with thrombocytopenia syndrome (SFTS) is a zoonotic disease with a high mortality rate for humans and cats. The clinical course and prognosis of SFTS in dogs remains unclear. In the present study, we investigated the clinical and epidemiological characteristics of SFTS virus (SFTSV) infection in dogs. All evaluated dogs exhibited an acute course and symptoms including fever (57.1%), anorexia (57.1%), depression (42.9%), and vomiting (35.7%). Thrombocytopenia was present in 45.5% of dogs, while jaundice was not observed. C-reactive protein, alanine transaminase, and alkaline phosphatase were elevated in some cases. Viral clearance occurred within 6 to 26 days. Phylogenetic analysis revealed that the SFTSV sequences were consistent with viruses circulating in the Republic of Korea. As dogs often live in close contact with humans, awareness of the clinical and epidemiological features of SFTS in dogs is crucial. Further large-scale studies are necessary to investigate SFTSV infection in dogs.

Immune escape mechanisms of severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome (SFTS), which is caused by SFTS virus (SFTSV), poses a serious threat to global public health, with high fatalities and an increasing prevalence. As effective therapies and prevention strategies are limited, there is an urgent need to elucidate the pathogenesis of SFTS. SFTSV has evolved several mechanisms to escape from host immunity. In this review, we summarize the mechanisms through which SFTSV escapes host immune responses, including the inhibition of innate immunity and evasion of adaptive immunity. Understanding the pathogenesis of SFTS will aid in the development of new strategies for the treatment of this disease.

Overview of the immunological mechanism underlying severe fever with thrombocytopenia syndrome (Review)

Severe fever with thrombocytopenia syndrome (SFTS) has been acknowledged as an emerging infectious disease that is caused by the SFTS virus (SFTSV). The main clinical features of SFTS on presentation include fever, thrombocytopenia, leukocytopenia and gastrointestinal symptoms. The mortality rate is estimated to range between 5-30% in East Asia. However, SFTSV infection is increasing on an annual basis globally and is becoming a public health problem. The transmission cycle of SFTSV remains poorly understood, which is compounded by the pathogenesis of SFTS not being fully elucidated. Since the mechanism underlying the host immune response towards SFTSV is also unclear, there are no effective vaccines or specific therapeutic agents against SFTS, with supportive care being the only realistic option. Therefore, it is now crucial to understand all aspects of the host-virus interaction following SFTSV infection, including the antiviral states and viral evasion mechanisms. In the present review, recent research progress into the possible host immune responses against SFTSV was summarized, which may be useful in designing novel therapeutics against SFTS.

Effects of corticosteroids treatment in patients with Severe Fever with Thrombocytopenia Syndrome:A single-center retrospective cohort study

OBJECTIVES

To evaluate the effect and safety of corticosteroids(CS) treatment in patients with severe fever with thrombocytopenia syndrome(SFTS).

METHODS

Patients with and without CS were retrospectively compared by COX regression and 1:1 propensity score matching analysis to evaluate the effects of CS on mortality and secondary infections in patients with SFTS.

RESULTS

A total of 467 SFTS patients were enrolled in the cohort study, there were 52 fatal cases and 415 nonfatal cases,the overall fatality rate was 11.1%. The mortality were observed in 36/144 (25%) and 16/323 (5%) patients in the CS-treated and non-CS-treated groups,respectively (P<0.001).Multivariate cox regression analysis showed that the difference was not statistically significant for CS treatment in the fatality (P>0.05, aHR 1.003, 95%CI 0.49-2.06).Difference in survival time between CS-treated and non-CS-treated groups after propensity score matching had no statistically significant (Log-Rank test P=0.390),whereas there was a significant difference in secondary infections between the CS-treated and non-CS-treated groups (P=0.007).

CONCLUSIONS

Although the CS treatment had no influence on fatality in patients with SFTS, it increased the risk of secondary infections.Administration of CS in patients with SFTS should be carefully considered and take into account the balance between therapeutic efficacy and adverse effects.

Clinical laboratory parameters and fatality of Severe fever with thrombocytopenia syndrome patients: A systematic review and meta-analysis

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease with high case fatality rate. Unfortunately, no vaccine or antiviral specifically targeting SFTS virus (SFTSV) are available for the time being. Our objective was to investigate the association between clinical laboratory parameters and fatality of SFTS patients.

Methods

The systematic review was conducted in accordance with The Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines. We searched (from inception to 24th February 2022) Web of Science, PubMed, National Knowledge Infrastructure databases and Wan Fang Data for relevant researchers on SFTS. Studies were eligible if they reported on laboratory parameters of SFTS patients and were stratified by clinical outcomes. A modified version of Newcastle-Ottawa scale was used to evaluate the quality of included studies. Standardized mean difference (SMD) was used to evaluate the association between laboratory parameters and outcomes. The between-study heterogeneity was evaluated quantitatively by standard Chi-square and the index of heterogeneity (I2). Heterogeneity was explored by subgroup and sensitivity analyses, and univariable meta-regression. Publication bias was determined using funnel plots and Egger’s test.

Results

We identified 34 relevant studies, with over 3300 participants across three countries. The following factors were strongly (SMD>1 or SMD<-0.5) and significantly (P<0.05) associated mortality: thrombin time (TT) (SMD = 1.53), viral load (SMD = 1.47), activated partial-thromboplastin time (APTT) (SMD = 1.37), aspartate aminotransferase (AST) (SMD = 1.19), lactate dehydrogenase (LDH) (SMD = 1.13), platelet count (PLT) (SMD = -0.47), monocyte percentage (MON%) (SMD = -0.47), lymphocyte percentage (LYM%) (SMD = -0.46) and albumin (ALB) (SMD = -0.43). Alanine aminotransferase, AST, creatin phosphokinase, LDH, PLT, partial-thromboplastin time and viral load contributed to the risk of dying of SFTS patients in each subgroup analyses. Sensitivity analysis demonstrated that the results above were robust.

Conclusions/significance

The abnormal levels of viral load, PLT, coagulation function and liver function, significantly increase the risk of SFTS mortality, suggesting that SFTS patients with above symptoms call for special concern.

The Endless Wars: Severe Fever With Thrombocytopenia Syndrome Virus, Host Immune and Genetic Factors

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging arboviral infectious disease with a high rate of lethality in susceptible humans and caused by severe fever with thrombocytopenia syndrome bunyavirus (SFTSV). Currently, neither vaccine nor specific antiviral drugs are available. In recent years, given the fact that both the number of SFTS cases and epidemic regions are increasing year by year, SFTS has become a public health problem. SFTSV can be internalized into host cells through the interaction between SFTSV glycoproteins and cell receptors and can activate the host immune system to trigger antiviral immune response. However, SFTSV has evolved multiple strategies to manipulate host factors to create an optimal environment for itself. Not to be discounted, host genetic factors may be operative also in the never-ending winning or losing wars. Therefore, the identifications of SFTSV, host immune and genetic factors, and their interactions are critical for understanding the pathogenic mechanisms of SFTSV infection. This review summarizes the updated pathogenesis of SFTS with regard to virus, host immune response, and host genetic factors to provide some novel perspectives of the prevention, treatment, as well as drug and vaccine developments.

Clinical Characteristics and Immune Status of Patients with Severe Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is a novel infectious disease caused by bunya virus. The purpose of this study was to investigate the clinical characteristics of SFTS patients and their virus-related immune disorders in vivo. Patients with SFTS admitted to Nanjing Drum Tower Hospital from 2017 to 2020 were retrospectively analyzed, and divided into survival group and death group according to the 28-day survival. Clinical characteristics and laboratory examination results of SFTS patients were recorded, and dynamic changes of immune function and inflammatory factors were statistically analyzed. Prolonged activated prothrombin time (APTT) (p = 0.001), high viral load (p = 0.001), and elevated human leukocyte antigen DR (HLA-DR) level (p = 0.002) were independent prognostic risk factors for SFTS patients. Compared to the survival group, the nonsurvival group was more prone to hemorrhagic and neurological symptoms (p < 0.05). Natural kill (NK) cell count, interleukin-10, interferon-α, and tumor necrosis factor-α scores in the nonsurvival group continued to increase after admission, while CD3+ T, CD4+ T, and CD8+ T cell counts continued to decrease. CD3+ T lymphocyte count was negatively correlated with viral load (R = 0.3883, p < 0.001), CD4+ T lymphocyte count was negatively correlated with viral load (R = 0.28933, p < 0.001), CD8+ T lymphocyte count was negatively correlated with viral load (R = 0.781, p < 0.001), and HLA-DR was positively correlated with viral load (R = 0.489, p < 0.001). High viral load, prolonged APTT time, and elevated HLA-DR level are independent prognostic risk factors for SFTS patients. The T lymphocyte subsets of SFTS patients continue to decrease after infection, and the number of T lymphocyte subsets can reflect the severity of the disease.

Expansion of granulocytic myeloid-derived suppressor cells in patients with severe fever with thrombocytopenia syndrome

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS), caused by novel bunyavirus (SFTSV) is a hemorrhagic fever with a high mortality rate of over 10%. We have previously shown that granulocytic myeloid-derived suppressor cell (gMDSC) might affect arginine metabolism which was associated with decreased platelet count and T lymphocyte dysfunction in this disease.

OBJECTIVES

The study was designed to investigate the expression of the gMDSCs subsets in SFTS patients, and to evaluate its association with disease severity.

METHODS

A prospective study was performed on 166 confirmed SFTSV infected patients. Sequential blood samples were collected during hospitalization and after recovery. SFTSV RNA was quantified by real-time RT-PCR. The gMDSCs and NK cells were determined by Flow cytometry analysis, which were associated with disease severity.

RESULTS

Elevation of the activated gMDSC was observed in SFTS patients at acute phase, with a significantly higher level of gMDSC attained in 79 severe and 29 fatal SFTS patients than in the mild patients. The NK cells were depleted at the early infection and not restored to normal level until four months after disease. The expansion of gMDSC was accompanied by the elevated expressions of CD3-ζ of NK and Arginase-1, in contrast with the decreased ROS in gMDSC. The levels of NK, CD3-ζ of NK, viral load and platelet count were significantly associated with the level of gMDSC.

CONCLUSIONS

Expansion of gMDSC was demonstrated in SFTS, which was associated with severe disease and suppressed antiviral NK cell via other mechanism than Arginase-1 or ROS. This article is protected by copyright. All rights reserved.

Neutrophil-to-lymphocyte ratio is associated with 28-day mortality in patients with severe fever with thrombocytopenia syndrome

Objectives

To determine the association of the neutrophil-to-lymphocyte ratio (NLR) with 28-day mortality in patients with severe fever with thrombocytopenia syndrome (SFTS).

Methods

A single-centre retrospective analysis was performed in an emergency department from January 01, 2018, to June 30, 2021. Univariate and multivariable Cox proportional hazards regression models were used to investigate the prognostic factors associated with 28-day mortality. Kaplan–Meier curves were analysed in patients stratified by the optimal cut-off point of the NLR determined using a receiver operating characteristic (ROC) curve.

Results

In total, 182 SFTS patients were included, and 24 (13.2%) died within 28 days. The median age of the included patients was 59.64 ± 12.74 years, and 48.4% (88/182) were male. The patients in the non-survival group had significantly higher NLRs than those in the survival group (6.91 ± 6.73 vs. 2.23 ± 1.83). The NLR was a significant predictor of 28-day mortality (adjusted HR: 1.121, 95% CI: 1.033, 1.215). The area under the ROC curve of the NLR for predicting 28-day mortality was 0.743 (95% CI: 0.624, 0.862), and the optimal cut-off value was 4.19 (sensitivity, 54.2%; specificity, 89.2%). In addition, 28-day mortality in the patients with an NLR ≥ 4.19 was notably higher than that in the patients with an NLR < 4.19 (43.3% vs. 7.2%), and Kaplan–Meier analysis showed that the patients with an NLR ≥ 4.19 had a significantly lower survival rate than those with an NLR < 4.19.

Conclusions

The NLR was a significant, independent predictor of 28-day mortality in SFTS patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07206-8.

Acute Myocarditis with Severe Fever and Thrombocytopenia Syndrome

A 67-year-old man, hospitalized with fever and pancytopenia, experienced cardiogenic shock on the 3rd day of hospitalization. He complained of chest pain and exhibited cardiac dysfunction, upregulated serum troponin levels, and an ST elevation on electrocardiogram. Severe fever with thrombocytopenia syndrome (SFTS) was suspected based on the symptom course after a tick bite and was definitively diagnosed using the serum polymerase chain reaction (PCR) test. An endomyocardial biopsy performed in the convalescent phase revealed a sign of myocardial inflammation with increases in CD3- and CD68-positive cells. We herein report the first case of acute myocarditis complicated with SFTS.

The Evaluation of Surrogate Laboratory Parameters for Predicting the Trend of Viral Loads in Patients with Severe Fever with Thrombocytopenia Syndrome: Cross-Correlation Analysis of Time Series

Background

There is a correlation between the severe fever with thrombocytopenia syndrome (SFTS) viral load and disease severity; however, measurement of viral load is difficult in general laboratory and it takes time to obtain a viral load value. Here, the laboratory parameters for predicting the dynamic changes in SFTS viral load were identified. In addition, we tried to evaluate a specific time point for the early determination of clinical deterioration using dynamic change of laboratory parameters.

Materials and Methods

This observational study included SFTS patients in Korea (2013 - 2020). Cross-correlation analysis at lagged values was used to determine the temporal correlation between the SFTS viral loads and time-series variables. Fifty-eight SFTS patients were included in the non-severe group (NSG) and 11 in the severe group (SG).

Results

In the cross-sectional analyses, 10 parameters -white blood cell, absolute neutrophil cell, lymphocyte, platelet, activated partial thromboplastin time (aPTT), C-reactive protein, aspartate aminotransferase (AST), alanine transaminase (ALT), lactate dehydrogenase (LDH), and creatine phosphokinase (CPK)- were assessed within 30 days from the onset of symptoms; they exhibited three different correlation patterns: (1) positive, (2) positive with a time lag, and (3) negative. A prediction score system was developed for predicting SFTS fatality based on age and six laboratory variables -platelet, aPTT, AST, ALT, LDH, and CPK- in 5 days after the onset of symptoms; this scoring system had 87.5% sensitivity and 86.0% specificity (95% confidence interval: 0.831 - 1.00, P <0.001).

Conclusion

Three types of correlation patterns between the dynamic changes in SFTS viral load and laboratory parameters were identified. The dynamic changes in the viral load could be predicted using the dynamic changes in these variables, which can be particularly helpful in clinical settings where viral load tests cannot be performed. Also, the proposed scoring system could provide timely treatment to critical patients by rapidly assessing their clinical course.

Sex Differences in Case Fatality Rate of Patients With Severe Fever With Thrombocytopenia Syndrome

Background: Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne disease with high mortality. However, detailed analysis is lacking to explore the complex effect of sex with age or comorbidities. Methods: A retrospective cohort study was performed among 2,938 SFTS patients entered during 2011-2020 in Xinyang, China. The case fatality rate (CFR) was estimated for their association with sex, age, and comorbidities by an interactive way. The difference of immune response between sex was explored in an age dependent way. Results: An overall CFR of 15.3% (450/2,938) was obtained, which appeared to be higher in males than in females [17.7% vs. 13.6%, adjusted odds ratio (aOR) = 1.24; 95% CI, 1.00-1.53; P = 0.048] and increased dramatically with age (P < 0.001). The associations between sex and SFTS fatal outcome were age-dependent and varied according to the status of comorbidities. The mortality-related risk conferred by older age was more pronounced in males, with aOR (95% CI) to be 5.76 (3.75-8.84) vs. 5.30 (3.54-7.95) in female. Sex-stratified analysis disclosed significant associations between death and comorbidities among female patients (aOR = 1.87, 95% CI: 1.40-2.49; P < 0.001), while none among males. Among females, the significant associations between presence of comorbidity and fatal outcome differed among age groups, with aOR (95% CI) decreased from 2.28 (1.16-4.46) in ≤60 years, to 2.06 (1.34-3.18) in 60-70 years and further to 1.55 (0.97-2.47) in >70 years. Altogether 194 SFTS patients were randomly selected for the test of B cells, natural killer (NK) cells, CD4 cells percentages, and anti-SFTSV IgM antibody level, the results revealed that males >60 years had significantly decreased percentages of B cells, CD4 cells, lower anti-SFTSV IgM antibody titer, and increased level of NK cells than male aged ≤60 years, while none of these age specific differences was observed in the females. This finding underlies the more pronounced age specific difference in CFR among male than female. Conclusions: Males had a significantly higher mortality of SFTS than did females, and more likely to be affected by aging for SFTS mortality. This difference can be explained by the effect from comorbidities and the host immunity. It is essential to take a sex- and age-based approach to SFTS treatment and management.

Clinical feature of severe fever with thrombocytopenia syndrome (SFTS)-associated encephalitis/encephalopathy: a retrospective study

BACKGROUND/OBJECTIVE

Severe fever with thrombocytopenia syndrome (SFTS) cause encephalitis/encephalopathy, but few reports were available. We aimed to investigate the incidence of encephalitis/encephalopathy in SFTS patients and to summarize clinical characteristics, laboratory findings and imaging features.

METHODS

We conducted a retrospective review of all patients with confirmed SFTS admitted to Nanjing Drum Tower Hospital, a tertiary hospital in Nanjing City, China, between January 2016 and July 2020. The patients were divided into two groups according to whether they had encephalitis/encephalopathy: encephalitis/encephalopathy group and non- encephalitis/encephalopathy group. Clinical data, laboratory findings, imaging characteristics, treatments and outcomes of these patients were collected and analyzed.

RESULTS

A total of 109 SFTS patients with were included, of whom 30 (27.5 %) developed encephalitis/encephalopathy. In-hospital mortality (43.3 %) was higher in encephalitis/encephalopathy group than non-encephalitis/encephalopathy group (12.7 %). Univariate logistic regression showed that cough, wheezing, dyspnoea, respiratory failure, vasopressors use, bacteremia, invasive pulmonary aspergillosis (IPA) diagnoses, PCT > 0.5 ug/L, CRP > 8 mg/L, AST > 200 U/L and serum amylase level > 80 U/L were the risk factors for the development of encephalitis/encephalopathy for SFTS patients. Multivariate logistic regression analysis identified bacteremia, PCT > 0.5 mg/L and serum amylase level > 80 U/L as independent predictors of encephalitis/ encephalopathy development for SFTS patients.

CONCLUSIONS

SFTS-associated encephalitis/encephalopathy has high morbidity and mortality. it was necessary to strengthen the screening of CSF testing and brain imaging after admission for SFTS patients who had symptoms of encephalitis/encephalopathy. SFTS patients with bacteremia, PCT > 0.5 ug/L or serum amylase level > 80 U/L should be warned to progress to encephalopathy.

Clinical Update of Severe Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is an acute febrile illness characterized by fever, leukopenia, thrombocytopenia, and gastrointestinal symptoms such as diarrhea, nausea, and vomiting resulting from infection with the SFTS virus (SFTSV). The SFTSV is transmitted to humans by tick bites, primarily from Haemaphysalis longicornis, Amblyomma testudinarium, Ixodes nipponensis, and Rhipicephalus microplus. Human-to-human transmission has also been reported. Since the first report of an SFTS patient in China, the number of patients has also been increasing. The mortality rate of patients with SFTS remains high because the disease can quickly lead to death through multiple organ failure. In particular, an average fatality rate of approximately 20% has been reported for SFTS patients, and no treatment strategy has been established. Therefore, effective antiviral agents and vaccines are required. Here, we aim to review the epidemiology, clinical manifestations, laboratory diagnosis, and various specific treatments (i.e., antiviral agents, steroids, intravenous immunoglobulin, and plasma exchange) that have been tested to help to cope with the disease.

Early-Warning Immune Predictors for Invasive Pulmonary Aspergillosis in Severe Patients With Severe Fever With Thrombocytopenia Syndrome

Aspergillus-related disease was confirmed to be associated with immune disorders in patients, severe patients with severe fever with thrombocytopenia syndrome (SFTS) infected by novel phlebovirus were confirmed to have severe immune damage including cellular immunosuppression and cytokine storms. Secondary invasive pulmonary aspergillosis (IPA) in severe SFTS patients can increase fatality rate. This study investigated early-warning predictive factors of secondary IPA in severe SFTS patients. Receiver operating characteristic analysis was used to assess the value of immune parameters to predict IPA in SFTS patients. The cut-off values of CD4⁺ and CD8⁺ T-cell counts to predict IPA were 68 and 111 cells/mm³, with sensitivities of 82.6% and 72%, and specificities of 56.7% and 83.3%, respectively. Cut-off values of IL-6, TNF-α, IL-8, and IL-10 to predict IPA incidence in critically ill SFTS patients were 99 pg/mL, 63 pg/mL, 120 pg/mL, and 111 pg/mL, with sensitivities of 90.0%, 86.7%, 83.3% and 90.0% and specificities of 80.4%, 71.7%, 82.6% and 65.2%, respectively. Lower CD4⁺ and CD8⁺ T-cells counts, higher levels of IL-6, TNF-α, IL-8 and IL-10, higher incidence of pancreatic and renal damage, early antibacterial therapy of carbapenems, and intensive care unit admission were risk factors of IPA in SFTS patients. Multivariate logistic regression analysis indicated counts of CD4⁺ T-cells <68 cells/mm³ combined with CD8⁺ T-cells <111 cells/mm³ (odds ratio [OR] 0.218, 95% confidence interval [CI] 0.059–0.803, p=0.022), IL-6 >99 pg/ml combined with IL-10 >111 pg/ml (OR 17.614, 95% CI 2.319–133.769, p=0.006), and brain natriuretic peptide level >500 pg/ml (OR 13.681, 95% CI 1.994–93.871, p=0.008) were independent risk factors for IPA in SFTS patients. The mortality in the IPA group was significantly higher than in the non-IPA group (p=0.001). Early antifungal treatment of IPA patients was significantly associated with improved survival (log-rank, p=0.022). Early diagnosis of IPA and antifungal treatment can improve the prognosis of SFTS patients. Besides, we speculate SFTS may be as a host factor for IPA.

A new emerging pandemic of severe fever with thrombocytopenia syndrome (SFTS)

The aim of this study is to make aware every one of the deadliest diseases named severe fever with thrombocytopenia syndrome (SFTS). It has become the worldwide pandemic in recent few years. It is a kind of haemorrhagic fever, caused by SFTS virus (SFTSV), a novel phlebovirus of family Bunyaviridae. This syndrome is also a tick-borne zoonosis that means the virus transmitted from tick bite (having virus) into human body, i.e. infection spread from animals to humans and also transmitted from human to human. Epidemiological data of SFTS was collected to know the nature/symptoms of SFTSV. First case of this disease has been reported in China, followed by Japan, South korea, Taiwan, USA and many other countries. Vertebrates are the host of this disease and tick functions as a vector, where the virus can undergo brisk changes using gene mutation, homologous recombination and reassortments. The major symptoms of hemorrhagic fever are fever, thrombocytopenia, leucopenia and gastrointestinal abnormalities. Sometimes in very severe cases, full body organ failure may also take place and average death rate in humans is nearly 10 %. Old aged peoples are more prone to SFTSV infection. Apart from the fact of increasing SFTSV related health problems to humans, the pathogenesis of SFTS virus in human is not entirely understood and no treatment to this virus is still available. The simplest way to protect our self from this infection is to refrain from tick bite. Therefore, this disease has evolved to produce serious health issues to humans in various countries of world including china. This review discussing about causative agent, epidemiology, pathogenesis, diagnosis and treatment of SFTS. In order to control the spread of SFTSV, we have to stop the viral transmission or to protect the easily vulnerable population from tick bites, avoiding direct contact of infectious and also to use personal protective devices for SFTS patients. So, the weather conditions, mode of transmission and creation of new therapeutics like vaccines and drugs are the main areas of forthcoming research.

Invasive pulmonary aspergillosis is a frequent complication in patients with severe fever with thrombocytopenia syndrome: A retrospective study

OBJECTIVES

Invasive pulmonary aspergillosis (IPA) usually occurs in immunocompromised hosts. It has recently been reported that patients with severe fever with thrombocytopenia syndrome (SFTS) can also develop IPA. The aim of this study was to determine the incidence of IPA in SFTS patients and to investigate the relevant clinical, imaging, and laboratory characteristics.

METHODS

A retrospective review was conducted of all patients with SFTS admitted to Nanjing Drum Tower Hospital, a tertiary hospital in Nanjing City, China, between January 2016 and December 2019. The patients were divided into two groups according to whether they had IPA: the IPA group and the non-IPA group. Data on clinical manifestations, laboratory findings, imaging characteristics, treatments, and outcomes were collected and analysed.

RESULTS

A total of 91 SFTS patients were included, of whom 29 (31.9%) developed IPA. In-hospital mortality (22.0%) was higher in the IPA group than in the non-IPA group. Univariate logistic regression showed that diabetes, cough, wheezing, amylase level, vasopressor use, encephalopathy, and intensive care unit transfer were risk factors for the development of IPA. Multivariate logistic regression analysis identified wheezing as an independent predictor of IPA in SFTS patients.

CONCLUSIONS

SFTS combined with IPA is associated with high morbidity and mortality. It is necessary to strengthen screening for fungal infections after admission in SFTS patients. However, whether early antifungal prophylaxis should be administered needs further investigation.

Baseline mapping of severe fever with thrombocytopenia syndrome virology, epidemiology and vaccine research and development

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a newly emergent tick-borne bunyavirus first discovered in 2009 in China. SFTSV is a growing public health problem that may become more prominent owing to multiple competent tick-vectors and the expansion of human populations in areas where the vectors are found. Although tick-vectors of SFTSV are found in a wide geographic area, SFTS cases have only been reported from China, South Korea, Vietnam, and Japan. Patients with SFTS often present with high fever, leukopenia, and thrombocytopenia, and in some cases, symptoms can progress to severe outcomes, including hemorrhagic disease. Reported SFTSV case fatality rates range from ~5 to >30% depending on the region surveyed, with more severe disease reported in older individuals. Currently, treatment options for this viral infection remain mostly supportive as there are no licensed vaccines available and research is in the discovery stage. Animal models for SFTSV appear to recapitulate many facets of human disease, although none of the models mirror all clinical manifestations. There are insufficient data available on basic immunologic responses, the immune correlate(s) of protection, and the determinants of severe disease by SFTSV and related viruses. Many aspects of SFTSV virology and epidemiology are not fully understood, including a detailed understanding of the annual numbers of cases and the vertebrate host of the virus, so additional research on this disease is essential towards the development of vaccines and therapeutics.

Severe fever with thrombocytopenia syndrome: a systematic review and meta-analysis of epidemiology, clinical signs, routine laboratory diagnosis, risk factors, and outcomes

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with the high case-fatality rate, and lack of vaccines. We aimed to systematically analysed the epidemiological characteristics, clinical signs, routine laboratory diagnosis, risk factors, and outcomes.

Methods

Documents on SFTS were collected by searching the Chinese National Knowledge Infrastructure, Wan Fang Data, PubMed, Embase, and Web of Science databases from 2011 to 2018. Meta-analysis was performed by using Review Manager and Stata software.

Results

Twenty-five articles involving 4143 cases were included. Diarrhea (odds ratio (OR) =1.60, 95% confidence interval (CI): 1.06 to 2.42, P = 0.02), and vomiting (OR = 1.56, 95% CI: 1.01 to 2.39, P = 0.04) on admission were associated with the fatal outcomes of SFTS. Compared to patients with mild symptoms, patients with severe symptoms had significantly elevated levels of lactic acid dehydrogenase (standard mean difference (SMD) =1.27, 95% CI: 0.59 to 1.94), alanine aminotransferase (SMD = 0.55, 95% CI: 0.24 to 0.85), aspirate aminotransferase (SMD = 1.01, 95% CI: 0.69 to 1.32), and creatine kinase (SMD = 1.04, 95% CI: 0.74 to 1.33) but had reduced platelet counts (SMD = -0.87, 95% CI: − 1.16 to − 0.58) and albumin levels (SMD = -1.00, 95% CI: − 1.32 to − 0.68). The risk factors for poor prognosis included age (mean difference (MD) =6.88, 95% CI: 5.41 to 8.35) and farming (OR = 2.01, 95% CI: 1.06 to 3.80). For the risk factors of contracting SFTS, the incidence of SFTS related to tick bites was 24% [95% CI: 0.18 to 0.31]. The pooled case-fatality rate of SFTS patients was 18% [95% CI: 0.16 to 0.21].

Conclusions

China is the country with the highest incidence of SFTS. May to July was the peak of the epidemic, and farmers were a high-risk group. The risk factor for SFTS included age (poor prognosis) and tick bites (contracting SFTS). Patients with severe diarrhea and vomiting symptoms on admission should be noted. Clinicians could use routine laboratory parameters and clinical symptoms as references for clinically suspected cases, classification of SFTS, and timely treatment, especially in basic hospitals.

Depletion but Activation of CD56dimCD16+ NK Cells in Acute Infection with Severe Fever with Thrombocytopenia Syndrome Virus

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with high mortality (12%-30%). The mechanism by which the SFTS bunyavirus (SFTSV) causes severe illness remains unclear. To evaluate the phenotypic and functional characteristics of the NK cell subsets in SFTS patients, twenty-nine SFTS patients were sequentially sampled from admission until recovery. Phenotypic and functional characteristics of NK cell subsets in circulating blood were analysed via flow cytometry. Then, correlations between NK cell subset frequencies and the SFTS index (SFTSI) were evaluated in all SFTS patients (15 mild, 14 severe) upon admission. The frequencies of CD56^dimCD16⁺ NK cells were greatly decreased in early SFTSV infection and were negatively correlated with disease severity. Additionally, higher Ki-67 and granzyme B expression and relatively lower NKG2A expression in CD56^dimCD16⁺ NK cells were observed in acute infection. Moreover, the effector function of CD56^dim NK cells was increased in the acute phase compared with the recovery phase in nine severe SFTS patients. Additionally, interleukin (IL)-15, interferon (IFN)-α, IL-18 and IFN-γ secretion was markedly increased during early infection. Collectively, despite depletion of CD56^dimCD16⁺ NK cells, activation and functional enhancement of CD56^dimCD16⁺ NK cells were still observed, suggesting their involvement in defence against early SFTSV infection.

Preexisting chronic conditions for fatal outcome among SFTS patients: An observational Cohort Study

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease that is caused by a novel bunyavirus SFTSV. Currently our knowledge of the host-related factors that influence the pathogenesis of disease is inadequate to allow prediction of fatal outcome. Here we conducted a prospective study of the largest database on the SFTS patients, to identify the presence of comorbidities in SFTS, and estimate their effect on the fatal outcome. Among 2096 patients eligible for inclusion, we identified nine kinds of comorbidities, from which hyperlipidemia (12.2%; 95% CI: 10.8%–13.6%), hypertension (11.0%; 95% CI: 9.6%–12.3%), chronic viral hepatitis (CVH) (9.3%; 95% CI: 8.1%–10.5%), and diabetes mellitus (DM) (6.8%; 95% CI: 5.7%–7.9%) were prevalent. Higher risk of death was found in patients with DM (adjusted OR = 2.304; 95% CI: 1.520–3.492; P<0.001), CVH (adjusted OR = 1.551; 95% CI: 1.053–2.285; P = 0.026) and chronic obstructive pulmonary diseases (COPD) (adjusted OR = 2.170; 95% CI: 1.215–3.872; P = 0.009) after adjusting for age, sex, delay from disease onset to admission and treatment regimens. When analyzing the comorbidities separately, we found that the high serum glucose could augment diseases severity. Compared to the group with max glucose < 7.0 mmol/L, patients with glucose between 7.0–11.1 mmol/L and glucose ≥11.1 mmol/L conferred higher death risk, with the adjusted OR to be 1.467 (95% CI: 1.081–1.989; P = 0.014) and 3.443 (95% CI: 2.427–4.884; P<0.001). Insulin therapy could effectively reduce the risk of severe outcome in DM patients with the adjusted OR 0.146 (95% CI: 0.058–0.365; P<0.001). For CVH patients, severe damage of liver and prolongation of blood coagulation time, as well as high prevalence of bleeding phenotype were observed. These data supported the provocative hypothesis that treating SFTS related complications can attain potentially beneficial effects on SFTS.

SFTS now brings about a substantial global public health concern. Preexisting chronic conditions were thought to increase risk of severe SFTSV infections, however with sparse data mining efforts. In this study, we quantified the frequency of chronic comorbidities in SFTS, estimated their contribution to disease severity, and separately evaluated the effect from diabetes mellitus and chronic viral hepatitis on resulting in fatal outcome.

Cutaneous histopathology of the tick-bite region in severe fever with thrombocytopenia syndrome

A case of severe fever with thrombocytopenia syndrome (SFTS) in which a skin biopsy from the tick-bite region was analyzed is reported. The patient was a 72-year-old woman who developed fever and thrombocytopenia after a tick bite. SFTS was diagnosed from polymerase chain reaction (PCR) analysis of a blood sample. Histopathological analysis of a skin biopsy specimen from the tick-bite region showed CD20-positive perivascular and interstitial immunoblastic cells, which were positive to anti-SFTS virus (SFTSV) nucleoprotein antibody. In addition, SFTSV RNA was detected by real-time PCR from this biopsy specimen. Moreover, hemophagocytosis was also found in the tick-bite region. To the best of our knowledge, this is the first report to analyze the details of the tick-bite region of skin in SFTS, and the first to detect virus-infected cells in the skin. The present findings may help elucidate the mechanisms of entry of SFTSV.

Fulminant myocarditis associated with severe fever with thrombocytopenia syndrome: a case report

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging viral infectious disease with high mortality. It causes multiple organ dysfunction; however, myocarditis has never been reported as a complication with SFTS.

Case presentation

A 62-year-old previously healthy woman developed fever, fatigue, diarrhea, and a mild consciousness disorder. She visited a local clinic, and laboratory data showed leukocytopenia, thrombocytopenia, and elevation of the aspartate aminotransferase level. She was transferred to Kagoshima University Hospital and diagnosed as having SFTS by real-time reverse transcription polymerase chain reaction. Subsequently, her blood pressure gradually decreased despite fluid resuscitation and vasopressor administration. Based on elevated toroponin I levels in serum, a transient diffuse left ventricular hypokinesis and wall thickening in echocardiography, diffuse ST elevation in electrocardiography, and exclusion of other heart diseases, she was diagnosed as having fulminant myocarditis. After hemodynamic support with inotropic agents, she recovered near normal cardiac function. She was discharged to home on day 28.

Conclusions

We report the first case of fulminant myocarditis associated with SFTS.

The proportion, origin and pro-inflammation roles of low density neutrophils in SFTS disease

Background

Severe fever with thrombocytopenia syndrome (SFTS) is a novel emerging viral infectious disease. We explored the percentage, origins and functional roles of low density neutrophils (LDNs), one of the neutrophils subsets, in SFTS.

Methods

The LDNs and normal density neutrophils (NDNs) from blood of SFTS and normal volunteers which were collected separately. The percentage, origins and the phagocytic capability of SFTS viral (SFTSV) of LDNs were investigated by flow cytometry and real time PCR. The capacity of LDNs to secrete cytokines and to damage endothelial cells was assessed by ELISA and flow cytometry.

Results

We observed that the proportion of LDNs increased dramatically compared with the healthy donors and became the dominant circulating neutrophil population in SFTS patients. Interestingly, the NDNs from the normal donors could switch to LDNs under the SFTS environment. Moreover, SFTSV load in LDNs was significantly higher than that of NDNs in the severe SFTS patients. In addition, the LDNs secreted much higher levels of pro-inflammatory cytokines than NDNs in SFTS and could induce endothelial cell injury.

Conclusion

The NDNs can be converted to LDNs. This conversion mechanism could become the source of LDNs. The LDNs in severe SFTS patient could engulf more SFTSV and exhibit pro-inflammation functions.

Trial registration

The Ethics Committee of Tongji Medical College, Huazhong University of Science and Technology (IORG No: IORG0003571) gave a final APPROVAL for the study.

CD4 T cell loss and Th2 and Th17 bias are associated with the severity of severe fever with thrombocytopenia syndrome (SFTS)

Severe fever with thrombocytopenia syndrome (SFTS) is a newly emerging infectious disease caused by a novel bunyavirus with high mortality. Immune suppression is thought to be crucial in disease progression. However, data on immune responses during SFTS are scarce. This study aimed to evaluate the changes in CD4 T-cell subsets throughout the entirety of infection and analyse their relationships with disease severity in SFTS patients. In parallel with CD4 T-cell depletion, decreased Th1, Th2 and Treg numbers, but comparable Th17-cell numbers, were observed in deceased patients compared with those in surviving patients. Additionally, increased Th2 and Th17-cell percentages in the residual CD4 T-cell population led to aberrant Th2/Th1 and Th17/Treg ratios, which were positively correlated with disease severity. Collectively, our data indicated that CD4 T-cell deficiency, Th2 and Th17 bias were closely correlated with the severity of SFTS, indicating therapeutic potential of early immune interventions to ameliorate disease severity.

Polymorphisms and haplotypes in the promoter of the TNF-α gene are associated with disease severity of severe fever with thrombocytopenia syndrome in Chinese Han population

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease that is caused by a novel bunyavirus, SFTSV. We assessed whether the single nucleotide polymorphisms (SNPs) in the tumor necrosis factor-alpha (TNF-α) were associated with risk to severity of SFTS. Five TNF-α SNPs (SNP1: T-1031C; SNP2: C-863A; SNP3: C-857T; SNP4: G-308A; SNP5: G-238A) were genotyped in 987 hospitalized SFTS patients and 633 asymptomatic/mild SFTSV-infected subjects of Chinese Han origin. Multivariate logistic regression analysis was used to calculate adjusted odds ratios (ORs) and 95% confidence intervals (95% CIs). The hospitalized SFTS patients had significantly lower frequency of G-238A A allele than those with mild/asymptomatic infection (P = 0.006). Furthermore, T-1031C C allele (P < 0.001) and G-238A A allele (P < 0.001) were significantly associated with decreased risk of death. Multiple haplotypes were significantly associated with decreased risk of SFTS hospital admission (SNP1-2, CC; SNP1-3, CCC; SNP1-4, CCCG; SNP1-5, CCCGA; SNP2-4, CCGA; SNP3-5, CGA; SNP4-5, GA) and death (SNP1-2, CA; SNP1-3, CAG; SNP1-4, CACG; SNP1-5, CACGG; SNP2-3, AC; SNP2-4, ACG; SNP2-5, ACGG) after correction for multiple comparisons. By using the ELISA assay, we observed that TNF-α concentration of hospitalized patients was significantly increased in acute phase than in convalescent phase (P < 0.001). Elevated TNF-α concentration was also revealed from fatal patients (P < 0.001). The -238A allele was associated with decreased serum TNF-α levels in SFTS patients in acute phase (P = 0.01). Our findings suggest that polymorphisms in TNF-α gene may play a role in mediating the risk to disease severity of SFTS in Chinese Han population.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease that is caused by a novel bunyavirus. The current study disclosed the single nucleotide polymorphisms (SNPs) in the tumor necrosis factor-alpha (TNF-α) were associated with risk to disease severity of SFTS. These findings suggest that polymorphisms in TNF-α gene may play a role in mediating the risk to disease severity of SFTS in Chinese Han population. The study will be of interest to either the clinicians devoted to the prevention and therapy of SFTS or the geneticists devoted to studying the genetic susceptibility mechanisms of common diseases.

Association between peripheral γδ T cell subsets and disease progression of severe fever with thrombocytopenia syndrome virus infection

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease caused by SFTS virus. The cellular immune responses during SFTS virus infection have not been fully understood. This study examined the association between circulating γδ T cell subsets and clinical outcome of SFTS patients from China. A total of 101 hospitalized SFTS patients and 28 healthy controls were enrolled. Peripheral blood was collected, and lymphocyte subgroups and γδ T cell frequencies were evaluated by flow cytometry analysis. Their association with patients' outcome was also investigated. Starting from Week 1, the Vδ1 cells of patients were increased to significantly higher level at Month 3 after disease onset than the controls (P < 0.05), followed by a decrease to the normal level in Year 1. In contrast, the Vδ2 cells displayed significant lower level than the controls from Week 2 to Year 1. On Week 2, the Vδ2 cells demonstrated a significant decrease in the severe patients than both the mild and controls (P < 0.05). The adverse disease progression is accompanied by the reduction of Vδ2 cells, suggesting the key role of Vδ2 cells in the disease progression.

Current status of Severe Fever with Thrombocytopenia Syndrome vaccine development

Severe Fever with Thrombocytopenia Syndrome (SFTS) is a new emerging tick-borne disease caused by the phlebovirus, SFTS virus (SFTSV). The virus was discovered in central China in 2009 and has since been identified in both Japan and South Korea. Significant progress has been made on the molecular biology of the virus, and this has been used to develop diagnostic assays and reagents. Less progress has been made on the epidemiology, maintenance and transmission, clinical manifestations, immunological responses, and treatment regimens. A number of animal models have been investigated but, to date, none recapitulate all the clinical manifestations seen in humans. Vaccine development is at an early discovery phase.

Dynamic changes in the immunological characteristics of T lymphocytes in surviving patients with severe fever with thrombocytopenia syndrome (SFTS)

OBJECTIVE

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with high mortality. T cell deficiency has recently been described, but the changes in T cell functionality during acute SFTS virus (SFTSV) infection and the mechanisms leading to T lymphocyte death remain largely unknown. This study was conducted to evaluate T cell functionality and the expression of apoptotic/proliferation and activation/inhibition markers during acute SFTSV infection.

METHODS

Twenty-eight surviving SFTS patients were sequentially sampled during their entire hospital stay. SFTSV RNA copies were investigated using real-time RT-PCR. The expression levels of apoptotic markers (annexin V and CD95) and proliferation and activation markers (Ki-67, HLA-DR, and CD25) and the expression levels of programmed cell death-1 (PD-1), interferon gamma (IFN-γ), and granzyme B in T cells were evaluated by flow cytometry for the SFTS patients.

RESULTS

In parallel with T cell depletion, higher annexin V and CD95 expression was observed in SFTS patients. Additionally, the expression levels of Ki-67, HLA-DR, CD25, and PD-1 and the levels of IFN-γ and granzyme B in T lymphocytes were markedly increased in the SFTS patients.

CONCLUSIONS

T cell proliferation, activation, and functional enhancement were apparent despite the observation of T cell apoptosis, suggesting that these processes are involved in the complex protective response to SFTSV infection.

Kinetics of viral load and cytokines in severe fever with thrombocytopenia syndrome

•

SFTS viremia persists until week 3 from the day of symptom onset.

•

The concentrations of inflammatory cytokines are elevated in SFTS patients.

•

IFN-α, IL-10, and IP-10 are associated with the initial cytokine storm.

Background

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease in China, Japan, and Korea, which is characterized by high fever, thrombocytopenia, and high mortality. It is hypothesized that a cytokine storm plays an important role in the pathophysiology of SFTS. However, limited data have been published on the detailed kinetics of the viral load and cytokine profiles throughout the course of this disease.

Objectives

We investigated the patterns of changes in cytokines and viral load in SFTS patients.

Study design

During the admission period of patients, RNA was extracted from plasma and quantified by reverse transcription polymerase chain reaction. In addition, cytokine bead arrays were performed for the 18 cytokines and chemokines selected for testing.

Results

The median time from admission to the negative conversion of SFTS viremia was 17.0 days. When censored patients were found to be negative for viral load at discharge, the median duration of viral shedding was 13.0 days (95% CI, 5.4–20.6). Interferon (IFN)-α, interleukin (IL)-10, and IFN-γ-induced protein (IP)-10 concentrations significantly increased in the early course of disease and then decreased during the hospital stay. However, the concentrations of tumor necrosis factor-α, IL-1β, IL-12p40, IL-13, IL-17A, Regulated on Activation and Normally T-cell Expressed and Secreted (RANTES), and vascular endothelial growth factor (VEGF) increased during the late course of disease. Initial IP-10 levels during hospital days 1–4 were the most significantly correlated with initial viral load (r = 0.88, P < .01).

Conclusion

SFTS viremia persisted until weeks 2–3 and was highly correlated with initial plasma IP-10 levels. In addition, IFN-α, IL-10, and IP-10 were associated with the initial cytokine storm in SFTS.

The Emergence of Severe Fever with Thrombocytopenia Syndrome Virus

Severe fever with thrombocytopenia syndrome (SFTS) is a newly recognized hemorrhagic fever disease found throughout Asia with a case fatality rate between 12% and 30%. Since 2009, SFTS has been reported in China throughout 14 Chinese Provinces. In addition, SFTS has been recognized in South Korea and Japan with the first confirmed cases reported in 2012. A similar disease, caused by the closely related Heartland virus, was also reported in the United States in 2009. SFTS is caused by SFTS virus, a novel tick-borne virus in the family Bunyaviridae, genus Phlebovirus. Unlike other mosquito- and sandfly-borne bunyaviruses, SFTS virus has not been extensively studied due to its recent emergence and many unknowns regarding its pathogenesis, life cycle, transmission, and options for therapeutics remains. In this review, we report the most current findings in SFTS virus research.

Risk factors associated with fatality of severe fever with thrombocytopenia syndrome: a meta-analysis

Severe fever with thrombocytopenia syndrome is an emerging life-threatening infectious disease identified in 2009. Given high case-fatality rate among patients with severe fever with thrombocytopenia syndrome, identification of the risk factors at acute phase associated with fatality is crucial for treatment. Therefore, we aimed to meta-analytically evaluate risk factors of fatal clinical outcome of severe fever with thrombocytopenia syndrome. 238 fatal cases and 873 non-fatal cases from 12 studies were included in this meta-analysis. Elder age and high viral load were significantly associated with fatal clinical outcome. Further, severe fever with thrombocytopenia syndrome patients with fatal clinical outcome had significantly reduced level of albumin and platelet count, higher level of serum alanine aminotransferase, aspirate aminotransferase, lactic acid dehydrogenase and creatinine phosphokinase, and prolonged activated partial thromboplastin time, comparing with mild patients. These disturbed parameters function as predictors to warn fatal clinical outcome of the disease. Moreover, ribavirin has a minimal impact to alleviate disease progression of severe fever with thrombocytopenia syndrome. In conclusion, our finding demonstrates a panel of factors associated with fatality of SFTS disease, which have important implications during clinical practice.

Severe fever with thrombocytopenia syndrome (SFTS) and SFTS virus

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne infectious disease caused by the SFTS virus (SFTSV), a novel phlebovirus reported to be endemic to China in 2011. In Japan, the first SFTS patient was identified during the autumn of 2012; since then, over 100 SFTS patients have been reported. The SFTSV has been identified throughout Japan over the past two years; however, SFTS patients are specifically localized to western Japan. The clinical symptoms of SFTS include fever, thrombocytopenia, leukocytopenia, gastrointestinal symptoms, and various other symptoms, including muscular symptoms, neurological abnormalities, and coagulopathy. SFTS is often accompanied by hemophagocytic syndrome. The histopathological findings are characterized by necrotizing lymphadenitis, with infiltration of the virus-infected cells to the local lymph nodes. Pathophysiological analyses of SFTS include studies regarding the kinetics of cytokine production and immune responses in patients with SFTS and in SFTSV-infection animal models. This article aimed to survey the history of SFTS in Japan and to review the clinical, epidemiological, and virological aspects of SFTS and SFTSV infection.